Local radio communication system

ABSTRACT

The invention relates to a local radio communication system comprising a central controller ( 9 ), several bases ( 7 ) which are connected to the controller and several terminals ( 5 ) which communicate with the bases. The bases ( 7 ) communicate with the terminals using a local radio communication protocol with time division multiple access. Said bases are adapted to real-time transmit chronological information to the controller releasing to the transmissions planned for said bases. The controller is adapted to determine if there is a risk of interferences occurring between the planned transmissions and to impose a chronology for said planned transmissions on the bases in order to limit said interferences.

[0001] The present invention relates to local radiocommunicationsystems.

[0002] More particularly, the invention relates to a localradiocommunication system comprising:

[0003] at least one central controller,

[0004] several bases connected to the controller and controlled by saidcontroller,

[0005] and several terminals, each communicating with at least one ofthe bases, according to a master/slave process where the base plays arole of master and the terminal plays a role of slave at least aftersetting up a radio link between said base and said terminal, the basescommunicating with the terminals according to the same time divisionmultiple access local radiocommunication protocol (for example theBLUETOOTH protocol or the DECT protocol), said protocol providing, foreach base, successive time slots during which either an uplinkinformation packet sent by a terminal to said base or a downlinkinformation packet sent by said base to said terminal are transmitted,and said base being adapted to determine in advance and impose plannedtransmissions between said base and said terminal, said plannedtransmissions comprising planned transmissions of downlink informationand planned slots of uplink information, where the terminal isauthorized to transmit an uplink information packet to the base, and atleast some of said bases being susceptible to reciprocal interference,preventing the reception by one of said bases of an uplink informationpacket when another of said bases is transmitting a downlink informationpacket.

[0006] Document WO-A-00/69186 describes an example of a localradiocommunication system of this type.

[0007] In a local radiocommunication system of this type, there is,however, a risk of interference between the transmission of an uplinkinformation packet from a terminal to a base and the transmission of adownlink information packet from a different base to a terminal (at thesame frequency or at an adjacent frequency).

[0008] Such interferences must be avoided since they render the uplinkinformation packets “inaudible” to the bases, due to the fact that theuplink information radio signals are generally received by a base with apower which is substantially weaker than the power of the downlinkinformation signals transmitted by a different base: the uplinkinformation packets thus lost must subsequently be retransmitted,thereby reducing the effective throughput of the radiocommunicationsystem.

[0009] The object of the present invention is, in particular, toeliminate this disadvantage by reducing the probability of interferencebetween uplink information packets and downlink information packets.

[0010] For this purpose, according to the invention, aradiocommunication system of the type concerned is characterized in thatthe different bases are adapted to transmit to the controller, in realtime, at least chronological information relating to transmissionsplanned by said bases, and in that said controller is adapted todetermine whether there is a risk of interferences occurring betweensaid planned transmissions, and to impose on the bases a chronology ofsaid planned transmissions which enables at least some of saidinterferences to be avoided.

[0011] Thanks to these measures, the controller makes it possible forthe majority of interferences between uplink and downlink connections tobe foreseen and avoided, taking account of the fact that the largemajority of downlink communications are planned in advance by the bases,and that the large majority of uplink communications are authorized bythe bases.

[0012] Optionally, one and/or the other of the following measures may beused in preferred embodiments of the invention:

[0013] the controller is adapted to synchronize the different basesamong themselves, in such a way that all said bases transmit more orless during the same time slots and receive more or less during the sametime slots (apart from the difference between the duration of thestandard-length information packets and the duration of the time slots,this difference being generally referred to as the guard time: in otherwords, slight differences between the start of the time slots of thedifferent bases may be tolerated or even imposed, provided that thesedifferences is less than the aforementioned guard time);

[0014] the radiocommunication protocol provides transmissions ofstandard-length information packets extending at most over one timeslot, and transmissions of long information packets extending over anumber of more than 1 successive time slots, the controller beingadapted to impose on the different bases that all the standard-lengthuplink information packets corresponding to all said bases aretransmitted during the same time slots alternately with other time slotsin which all the standard-length downlink information packetscorresponding to all said bases are transmitted;

[0015] the radiocommunication protocol provides that the terminals senduplink information packets to the bases solely in response to a downlinkinformation packet received from a base, and the controller is adapted:

[0016] when a base has to send a long information packet to a terminal,to prevent the other bases from sending to the other terminals adownlink information packet requesting a response for the duration ofthe transmission of said long information packet,

[0017] and, when a terminal has to send a long information packet to abase, to prevent the other bases from sending a downlink informationpacket for the duration of the transmission of this long informationpacket;

[0018] the controller has in its memory information indicating pairs ofbases susceptible to reciprocal interference, and is adapted to delay atleast some of the planned transmissions only between said basessusceptible to reciprocal interference, so as to avoid at least someinterferences;

[0019] the bases are adapted to each carry out measurements of thesignals respectively received when the other bases are transmitting aradio signal, the controller being adapted to determine said pairs ofbases susceptible to reciprocal interference on the basis of saidmeasurements;

[0020] the bases are adapted to transmit to the controller, in additionto the chronological information, planned frequency informationindicating the frequency at which the planned transmissions must takeplace, the controller has in its memory, for each pair of basessusceptible to reciprocal interference, information indicating pairs ofinterference frequencies at which said bases are susceptible tointerference, and said controller is adapted to delay at least some ofthe planned transmissions only for said planned frequenciescorresponding to a pair of interference frequencies between said basessusceptible to reciprocal interference, so as to avoid at least someinterferences;

[0021] the bases are adapted to transmit to the controller, in additionto the chronological information, planned transmission categoryinformation indicating at least whether the information to betransmitted is or is not voice, and the controller is adapted not todelay a planned voice transmission;

[0022] the different bases are disposed in the immediate vicinity of oneanother;

[0023] the controller and the bases are contained in the same unit;

[0024] the controller also acts as a concentrator and makes the basescommunicate with an external link;

[0025] the bases and the terminals are adapted to communicate accordingto-the BLUETOOTH protocol.

[0026] Other characteristics and advantages of the invention will becomeapparent in the following description of one of its embodiments,provided by way of a non-limiting example, with reference to theattached drawings.

[0027] In the drawings:

[0028]FIG. 1 shows a schematic view of a building equipped with aradiocommunication system according to one embodiment of the invention;

[0029]FIG. 2 is a block diagram of the communication system shown inFIG. 1,

[0030]FIG. 3 shows a graphical illustration of the signals exchangedbetween two bases and two terminals during a short space of time.

[0031] In the different figures, the same references refer to identicalor similar components.

[0032]FIG. 1 shows a local radiocommunication system according to oneembodiment of the invention, serving a location 2, such as a group ofoffices 3, or a residential location, or the like.

[0033] This local radiocommunication network comprises a central station4 (CS) which communicates via a radio link with several fixed or mobileterminals 5 according to a local radiocommunication protocol such as theBLUETOOTH protocol or the DECT protocol, or other protocol of the TDMA(time division multiple access) type. The invention will be describedbelow in the specific case of the BLUETOOTH protocol, by way of example,but said invention could be applied in a similar fashion to the DECTprotocol, or other protocol.

[0034] The terminals 5 may, for example, be cordless telephones,microcomputers, electronic books, digital television sets, etc.

[0035] These terminals 5 may:

[0036] if necessary, dialog with one another via the central station 4,

[0037] or communicate with the outside, still via said central station 4which has a telecommunications link 6 to a public telecommunicationsnetwork. It will be noted that the link 6 may be either a wired link ora wireless link, for example a radio link.

[0038] As shown in FIG. 2, the central station 4 comprises several bases7 (B1-B3) connected to a central controller 9 (CONTR.) which controlssaid bases 7 as will be explained below and which, in the example shown,further acts as a concentrator and is connected to the aforementionedlink 6 via an interface 10 (INT.) comprising, for example, a modem orthe like.

[0039] The controller 9 is an electronic circuit comprising inparticular a microprocessor MP connected to a memory M.

[0040] The bases 7, for their part, are fixed bases adapted tocommunicate with the terminals 5 according to the chosenradiocommunication protocol, for example the BLUETOOTH protocol. Suchbases 7 are well known in the state of the art, as are the radiocircuits of the terminals 5.

[0041] The bases 7 are disposed in the immediate vicinity of oneanother, and the central station 4 preferably forms a single unit.

[0042] In the example shown, the bases 7 are each advantageously (butnot necessarily) equipped with a network of antennas 8 with controlleddirectivity, the electronic circuits of each base 7 then being adapted,in a manner known per se, to shift the phase of the different antennas 8of each base 7 in relation to one another so as to create spatialdirectivity for reception and transmission.

[0043] Given this directivity of the networks of antennas 8, and alsogiven the configuration of the location 2, each of the bases 7communicates with only some of the terminals 5 which are assigned to itwithin a cell, C1, C2, C3 respectively. Thus, in the example shown inFIGS. 1 and 2, the base Bi communicates with terminals T1, T2, T3, T4,T7, T8 and T10, the base B2 communicates with terminals T9, T11, T12,T13, T14, T15 and T16, and the base B3 communicates with terminals T5,T6.

[0044] The bases preferably transmit to the controller 9, at regulartime intervals, the identities of all the terminals 5 belonging to thelocal radiocommunication system, i.e. of all the terminals with whichthey respectively communicate (possibly only updates of this list may becommunicated to the controller 9 by the bases, for example when a baseloses the link with a terminal or when a base sets up a link to a newterminal).

[0045] In fact, when some of the terminals 5 are moved, for exampleterminals T9 and T11 in the example shown in FIGS. 1 and 2, theseterminals may, where appropriate, cease to communicate with the base 7to which they were previously assigned and may possibly communicate witha new base 7.

[0046] These changes of bases may be controlled, for example, by thecontroller 9, in particular according to the quality of thecommunication between each terminal 5 and each base 7.

[0047] Each base 7 communicates with the terminals 5 which are assignedto it according to a master/slave process where the base 7 plays therole of master once the radio link has been set up with thecorresponding terminal 5.

[0048] In this master/slave process, the base 7 controls thecommunication with each terminal 5 which is assigned to it, bycontrolling the use of successive time slots Si, Si+1, Si+2, etc. (seeFIG. 3), which are of a constant duration e with a value of 625 μs andwhich are each intended to enable the transmission of an informationpacket PI (or two information packets in the specific case of packetstransmitted in “PAGE” mode, transmitting only an identity code from abase to the terminals, or a portion of an information packet PI when apacket extending over several successive slots is involved).

[0049] In the example under consideration, where the radiocommunicationprotocol used is the BLUETOOTH protocol, each information packet PIcomprises an access code with a length of 72 bits, a header H with alength of 54 bits, and a payload part P, transporting, for example,voice and/or other information in digital form, with a length of between0 and 2745 bits. Moreover, the exchanges between bases and terminalstake place for each base in a frequency channel chosen from 80 availablechannels, determined by each base according to a andom process (thefrequency used is therefore known to each base after this randomdetermination).

[0050] In the most common case, each information packet PI is a standardinformation packet contained in a single time slot Si, with a durationslightly below the aforementioned duration θ, and the successive timeslots are assigned alternately:

[0051] to the transmissions by the base of downlink information packetsto the terminals 5 corresponding to this base,

[0052] and to the receptions by the base of uplink information packetstransmitted by the terminals assigned to this base.

[0053] Thus, in the example under consideration, the even time slots ofeach base 5 are assigned to the downlinks, i.e. to the transmissions ofdownlink information packets by this base, whereas the odd time slotsare assigned to the uplinks, i.e. to the receptions by the base ofuplink information packets originating from the terminals.

[0054] As shown in FIG. 3 in the simplified case of two bases Bj1, Bj2,each respectively communicating with a single terminal, Tk1, Tk2respectively, the controller 9 preferably imposes on the different bases7 a synchronization of their time slots Si, Si+1, Si+2 (possibly withslight accidental or deliberate differences between the starts of thetime slots of the different bases, less than the guard time, i.e. thanthe difference between the duration θ and the duration of a standardinformation packet), also so that the rows of time slots of thedifferent bases coincide with one another.

[0055] This measure already makes it possible for some of theinterferences between channels to be avoided, i.e. interferences betweenthe transmission of a downlink information packet by one of the bases 7,for example the base of the Bj1s, during the reception of an uplinkinformation packet by a different base, for example the base Bj2, inwhich case the reception of the uplink information packet is renderedimpossible given the much higher amplitude of the radio signalcorresponding to the downlink information packet in relation to theamplitude of the radio signal corresponding to the uplink informationpacket.

[0056] However, this measure is not adequate to prevent a sufficientfraction of the interferences between channels, since the bases 7 and/orthe terminals 5 may transmit large information packets extending overseveral successive time slots, in this case three time slots, or fivetime slots in the case of the BLUETOOTH radiocommunication protocol.

[0057] In this case, there is in fact a risk that one of the terminals 5will transmit an uplink information packet during the odd time slot orslots during which the transmission of a long downlink informationpacket by one of the bases 7 is taking place, in which case the, uplinkinformation packet concerned may not be received by the correspondingbase.

[0058] Similarly, when a long uplink information packet is transmittedby one of the terminals 5 to the corresponding base 7, there is a riskthat a different base 7 will transmit a downlink information packet inthe even time slot or in one of the even time slots during thetransmission of said long uplink information packet: in this case, thereis a risk that said uplink information data packet will be poorlyreceived by the corresponding base.

[0059] In the two cases envisaged here, a new transmission of theunreceived uplink information packet is necessary, which reduces thethroughput of the information system.

[0060] In order to overcome this disadvantage, the invention providesthat each base 7 transmits the chronology of its planned transmissionsand receptions in real time to the controller 9, this being possible dueto the fact that the bases 7 themselves control the communication withthe terminals 5 which are assigned to them (in particular the uplinkinformation packets are sent by the terminals in response to messagesreceived from the bases).

[0061] The controller 9 then determines in real time whether there is arisk of interference between the transmissions and the transmissionsplanned by the different bases 7. If such a risk of interference exists,the controller 9 imposes on the different bases 7 a chronology of theplanned transmissions (transmissions and/or receptions) enabling atleast some of said interferences, and preferably the totality of theseinterferences, to be avoided.

[0062] For example, the controller 9 forces one or more bases 7 to delaysome planned transmissions and/or receptions of information packets.

[0063] In particular, the controller may be adapted in such a way that:

[0064] when a base 7 has to send a long information packet (extendingover 3 or 5 time slots in the case of the BLUETOOTH protocol) to aterminal 5, it prevents the other bases from sending to the otherterminals 5 a downlink information packet requesting a response duringthe transmission of said long information packet,

[0065] and, when a terminal 5 has to send a long information packet to abase 7, it prevents the other bases from sending a downlink informationpacket during the transmission of this long information packet.

[0066] If necessary, the controller 9 may give priority to certaincategories of information transmissions. In particular, the bases 7 maytransmit to the controller 9 in real time, not only the chronology oftheir planned transmissions and receptions, but also the category of theinformation to be transmitted, in such a way as to indicate to thecontroller 9 particularly if the planned transmissions are intended totransport voice signals. In this case, the controller 9 may be adaptedto give priority to the transmissions of voice signals, generallycorresponding to telephone conversations, in such a way as to avoid theeffects of chopping of the transmitted voice signals.

[0067] Furthermore, the controller 9 may possibly, at regular timeintervals (for example at intervals of between 5 s and 1 h, orpreferably between 5 and 30 minutes), follow a process of adjustment ofthe networks of antennas 8 of the bases 7, instigating the transmissionof a test radio signal to each of the bases 7 in turn (in particular asignal in “PAGE” mode).

[0068] Depending on the modifications made in the electromagneticenvironment of the radiocommunication system 1 since the latestadjustment (moving of furniture, particularly metallic furniture,opening or closing of doors or windows, etc.), each base 7 may thenmodify the directivity of its antennas 8 during these transmissions inorder to minimize the signals received by the other bases 7, whileensuring that all of the bases 7 enable communication under goodconditions with all of the terminals 5 of the location 2 concerned.

[0069] During this adjustment process, when a base transmits a testradio signal, the level of the radio signal measured by the other basesis transmitted to the controller 9.

[0070] Moreover, each terminal which receives a test radio signal (inthis case an information packet in “PAGE” mode, according to theBLUETOOTH protocol) transmits a response to the base which transmittedthis signal, in such a way that this base knows the identity of all theterminals which are adapted to communicate with it in each of theantenna configurations under test. Moreover, each base measures thelevel of the response signal which it receives from each terminal whichhas responded to it, or, alternatively, the terminal measures the levelof the signal which it receives from each base and transmits this levelto the base in its response. These terminal identities and the signallevels thus measured are transmitted to the controller.

[0071] From the information thus collected during the adjustmentprocess, the controller may determine respective antenna configurationsof the different bases, thereby enabling minimization of the levels ofradio signals received by the bases during the transmission of said testradio signals, while ensuring that each terminal can communicate undergood conditions with at least one base with these adopted antennaconfigurations.

[0072] Finally, the controller 9 imposes the adopted antennaconfigurations on the bases 2 and indicates to them the identities ofthe terminals which are assigned respectively to them.

[0073] Moreover, once all the adjustments of the antenna networks arecompleted, depending on the levels of the radio signals received by thebases during the adjustment process and corresponding to the adjustmentsmade, the controller 9 determines and stores pairs of bases 7susceptible to reciprocal interference, i.e. pairs of bases 7 such thatthe transmission by one of these two bases of a downlink informationradio signal to a terminal 5 is susceptible to interfere with an uplinkinformation radio signal transmitted by a different terminal 5 to theother of these two bases, thereby preventing the good reception of theuplink information radio signal.

[0074] In this case, the controller 9 may advantageously be adapted todelay at least some of the planned transmissions only between said basessusceptible to reciprocal interference, in order to avoid theinterferences. Conversely, the controller 9 does not interfere with theplanned transmissions between bases which are not susceptible toreciprocal interference, thereby simplifying the work of said controllerand improving its speed.

[0075] The aforementioned measurements of the levels of radio signalsreceived by the bases 7 during the adjustment phase could possibly becarried out at the different frequencies permitted by the localradiocommunication protocol which is used, and the controller 9 may thendetermine and store pairs of frequencies susceptible to reciprocalinterference for each pair of bases 7 susceptible to reciprocalinterference.

[0076] In other words, the controller 9 stores, for each pair of bases 7susceptible to reciprocal interference, pairs of first and secondfrequencies in such a way that the transmission by one of these bases ofa radio signal at the first frequency prevents the good reception by theother base of a radio signal transmitted by a terminal 5 at the secondfrequency.

[0077] In the case envisaged above, the bases may be adapted to transmitto the controller in real time, in addition to the aforementionedchronological information of the planned transmissions, plannedfrequency information indicating the frequency at which the plannedtransmissions and receptions must take place, and said controller isadapted to delay at least some of the planned transmissions only forsaid planned frequencies corresponding to a pair of frequenciessusceptible to interfere between said bases susceptible to reciprocalinterference, so as to avoid the interferences.

[0078] It will be noted that, instead of comprising networks of antennas8 whose directivity is controlled by electronic means only, the bases 7could comprise one or more directive antennas 8 which can be moved byelectromechanical means.

[0079] Moreover, it will also be noted that some of the terminals 5could be beacons fixed at certain specific positions of the location 2,adapted to guarantee that the totality of said location falls wellwithin the radio coverage of the local radiocommunication network 1.

1. A local radiocommunication system comprising: at least one centralcontroller (9), several bases (7) connected to the controller (9) andcontrolled by said controller, and several terminals (5), eachcommunicating with at least one of the bases (7) according to amaster/slave process where the base (7) plays a role of master and theterminal plays a role of slave at least after setting up a radio linkbetween said base (7) and said terminal (5), the bases (7) communicatingwith the terminals (5) according to the same time division multipleaccess local radiocommunication protocol, said protocol providing, foreach base, successive time slots (Si) during which either an uplinkinformation packet (PI) sent by a terminal (5) to said base (7) or adownlink information packet (PI) sent by said base (7) to said terminal(5) are transmitted, and said base being adapted to determine in advanceand impose planned transmissions between said base and said terminal,said planned transmissions comprising planned transmissions of downlinkinformation and planned slots of uplink information, where the terminalis authorized to transmit an uplink information packet (PI) to the base,and at least some of said bases (7) being susceptible to reciprocalinterference, preventing the reception by one of said bases of an uplinkinformation packet (PI) when another of said bases is transmitting adownlink information packet (PI), characterized in that the differentbases (7) are adapted to transmit to the controller (9), in real time,at least chronological information relating to transmissions planned bysaid bases, and in that said controller (9) is adapted to determinewhether there is a risk of interferences occurring between said plannedtransmissions, and to impose on the bases (7) a chronology of saidplanned transmissions which enables at least some of said interferencesto be avoided.
 2. The local radiocommunication system as claimed inclaim 1, in which the controller (9) is adapted to synchronize thedifferent bases (7) among themselves, in such a way that all said basestransmit more or less during the same time slots (Si) and receive moreor less during the same time slots (Si+1).
 3. The localradiocommunication system as claimed in claim 2, in which theradiocommunication protocol provides transmissions of standard-lengthinformation packets (PI) extending at most over one time slot (Si), andtransmissions of information packets of a longer duration extending overan odd number of more than 1 successive time slots, the controller (9)being adapted to impose on the different bases that all thestandard-length uplink information packets (PI) corresponding to allsaid bases are transmitted during the same time slots alternately withother time slots in which all the standard-length downlink informationpackets (PI) corresponding to all said bases are transmitted.
 4. Thelocal radiocommunication system as claimed in claim 3, in which theradiocommunication protocol provides that the terminals send uplinkinformation packets to the bases solely in response to a downlinkinformation packet received from a base, and the controller is adapted:when a base has to send a long information packet to a terminal, toprevent the other bases from sending to the other terminals a downlinkinformation packet requesting a response for the duration of thetransmission of said long information packet, and, when a terminal hasto send a long information packet to a base, to prevent the other basesfrom sending a downlink information packet for the duration of thetransmission of this long information packet.
 5. The localradiocommunication system as claimed in any one of the preceding claims,in which the controller has in its memory information indicating pairsof bases (7) susceptible to reciprocal interference, and is adapted todelay at least some of the planned transmissions only between said basessusceptible to reciprocal interference, so as to avoid at least someinterferences.
 6. The local radiocommunication system as claimed inclaim 5, in which the bases (7) are adapted to each carry outmeasurements of the signals respectively received when the other bases(7) are transmitting a radio signal, the controller (9) being adapted todetermine said pairs of bases susceptible to reciprocal interference onthe basis of said measurements.
 7. The local radiocommunication systemas claimed in claim 5 or claim 6, in which: the bases (7) are adapted totransmit to the controller, in addition to the chronologicalinformation, planned frequency information indicating the frequency atwhich the planned transmissions must take place, the controller (9) hasin its memory, for each pair of bases (7) susceptible to reciprocalinterference, information indicating pairs of interference frequenciesat which said bases are susceptible to reciprocal interference, and saidcontroller (9) is adapted to delay at least some of the plannedtransmissions only for said planned frequencies corresponding to a pairof interference frequencies between said bases susceptible to reciprocalinterference, so as to avoid at least some interferences.
 8. The localradiocommunication system as claimed in any one of the preceding claims,in which the bases (7) are adapted to transmit to the controller, inaddition to the chronological information, planned transmission categoryinformation indicating at least whether the information to betransmitted is or is not voice, and the controller (9) is adapted not todelay a planned voice transmission.
 9. The local radiocommunicationsystem as claimed in any one of the preceding claims, in which thedifferent bases (7) are disposed in the immediate vicinity of oneanother.
 10. The local radiocommunication system as claimed in any oneof the preceding claims, in which the controller (9) and the bases (7)are contained in the same unit (4).
 11. The local radiocommunicationsystem as claimed in any one of the preceding claims, in which thecontroller also acts as a concentrator and makes the bases communicatewith an external link.
 12. The local radiocommunication system asclaimed in any one of the preceding claims, in which the bases (7) andthe terminals (5) are adapted to communicate according to the BLUETOOTHprotocol.